servegit: decompress input to git-upload-pack
Created by: keegancsmith
Ensure that if the Content-Encoding of a servegit request is gzip then we read it as a compressed input. git-upload-pack does not accept gzipped input and fails. This is only sometimes gzipped and I'm not sure of the conditions so we can't rely on it being always or never encoded.
This is a port of https://github.com/sourcegraph/sourcegraph/pull/21067
Co-authored-by: @efritz